A Novel Dissipativity-Based Control for Inexact Nonlinearity Cancellation Problems

When dealing with linear systems feedback interconnected with memoryless nonlinearities, a natural control strategy is making the overall dynamics linear at first and then designing a linear controller for the remaining linear dynamics. By canceling the original nonlinearity via a first feedback loop, global linearization can be achieved. However, when the controller is not capable of exactly canceling the nonlinearity, such control strategy may provide unsatisfactory performance or even induce instability. Here, the interplay between accuracy of nonlinearity approximation, quality of state estimation, and robustness of linear controller is investigated and explicit conditions for stability are derived. An alternative controller design based on such conditions is proposed and its effectiveness is compared with standard methods on a benchmark system

On the feasibility of dynamic substructuring for hybrid testing of vibrating structures

Abstract Dynamically substructured systems (DSS) are a typical technique to achieve real-time numerical simulations combined with physically tested components. However, the rigorous feasibility analysis before the implementation is missing. This paper is aimed to fill this gap by establishing rigorous conditions for when DSS is suitable for dynamic testing. The proposed method is based on novel symbolic recursive formulations for the transfer functions describing a generic lumped parameter vibrating structure, enabling the analysis of structural and other properties without requiring the computation of explicit symbolic expressions for the transfer functions involved, representing a significant breakthrough as it allows to perform feasibility analysis in analytical form, rather than solely relying on numerical approaches. The series of analytical conclusions presented in this paper, and future ones unlocked by the proposed approach, will significantly enrich the research in the community of DSS and structural vibrations. In particular, the proposed approach allows performing analysis of causality, controllability and observability using much reduced knowledge of the structure, thus significantly simplifying such analysis. Analytical conclusions on stability can also be made with the help of novel recursive form, removing the need of repeatedly calculating the roots of characteristic equations, a task that can be performed only via numerical approaches and for which analytical results are not available. The proposed methodology can be applied to a whole class of vibration problems and is not linked to any specific structure, going beyond the specific examples available in the literature.</jats:p

Open University vs. Consorzio Nettuno: An Institutional Analysis of Two Technology Enabled Higher Educational Systems

Assuming a rational perspective, the adoption and development of a new organisational technology can be viewed as a way to achieve an higher level of efficiency by finding the best way to fully exploit its potential. In other words, one might sustain that since organisations do initially ignore how to best deal with an innovative technology, they engage in a trial and error learning process that finally leads to the x-efficiency frontier. Once this knowledge is achieved, it will probably be spread around by external agents (e.g. consultants) enabling an imitative process. Thus in the long run all organisations will make almost the same efficient use of a mature organisational technology. In this paper we tried to explore how the same technology (eLearning) has been adopted by two diverse educational organisations. The patterns of development have been studied across time to verify if a progressive convergence has occurred. Results are providing some useful insights on what variables must be paid attention to when transferring a technological organisational innovation in a different settin